Mass flow controllers are used to regulate the amount of the process gas that is introduced into a manufacturing system, for example a semiconductor manufacturing system. With reference to FIG. 1, the gas will flow from a source through a gas path 10, commonly referred to as a gas stick, that can include, as an example, a regulator 12, a manual valve 14, a pressure transducer or sensor 16, a filter 18, an air operated isolation valve 20, an air operated valve purge valve 24, a mass flow controller 22, and a downstream isolation air operated valve 26 to the process chamber. This is an exemplary manufacturing system and any number of additional and alternative components could comprise the gas path from the source to the process chamber.
Mass flow controller 22, and other components that transport the gas from the source to the process chamber, often require heating during operation so that the process gas flowing through the mass flow controller does not condense back into liquid form. The temperature to which the components must be heated during operation depends on various factors, including the type of gas being transported, but the gas should not be allowed to change to a liquid state due to the deleterious effects on the process and the components in the manufacturing system. The heating of the components in the gas path has long been recognized as a requirement to enable proper operation of the components and equipment in various manufacturing processes, including semiconductor manufacturing. However, existing methods for heating the components in the gas transport path have several limitations.
One conventional method of heating the mass flow controller and other components in the gas transport path involved placing a heating blanket on a portion of the mass flow controller and/or other components. For example, a heating blanket 28 could surround the mass flow controller and/or the enter gas stick, as indicated by the shaded areas in FIG. 1. Some heating blankets 28 comprise a silicon rubber material having wires running through the material that would heat up as electrical current traveled through the wires. The heat from the heating blanket is transferred to the main body 30 of the mass flow controller 22, and subsequently into the interior of the mass flow controller 22 in order to heat the gas to prevent it from transforming to a liquid state.
This conventional method of heating the components in the gas path 10 has several limitations. The heating blanket is not especially efficient due to inefficiencies of transferring heat from the heating wires in the heating blanket, to the main body of the component, to the internal flow path within the mass flow controller and finally to the gas flowing through the component. Additionally, this conventional heating blanket method is difficult to implement for top mount mass flow controllers due to space constraints and design limitations that prevent the blanket from being positioned around the entire body of the mass flow controller.